Some printing groups operate without the use of dampening agents and are thus particularly suited to waterless web offset printing. When printing is being done, without the use of dampening agents, a printing plate which permits the transfer of the print image, without the use of dampening agents, is fastened to a plate cylinder of the printing group. The printing plate has a lower layer of an ink-absorbing material and an upper layer of an ink-repelling material. Ink-repelling at the upper layer of the printing plate takes place without dampening agents. Accordingly, special materials are required for use in producing the upper plate layer. Silicon-containing materials, in particular, have shown themselves to be suitable for use as an ink-repelling layer without the use of dampening agents.
The upper, and therefore the ink-repellent layer of the printing plate has openings in that layer with those openings being situated in the areas of the print image which are to be printed. The printing ink can thus collect on the ink-absorbing layer which is located underneath the ink-repellant layer. In printing groups of this type, the print image can be transferred, in this way, to a downstream-located transfer cylinder, such as, for example, a rubber blanket cylinder. The upper layer of the printing plate covers the lower layer in the areas of the print image which are not to be printed, so that no printing ink is transferred in these areas.
A printing group for waterless offset printing is described in WO 03/045695 A1, for example.
EP 0 182 156 B1 discloses a rubber blanket cylinder with an area whose radius has been reduced.
A rubber blanket whose ends taper is known from DE 198 02 470 A1.
DE 198 02 470 A1 discloses a multi-layered rubber blanket.
DE 33 15 506 A1 describes an offset blanket having a recess extending along an axial direction between its ends. This is provided in order to prevent plate edges from also being printed.
If several printing plates are fastened on the plate cylinder one behind the other, with their ends facing each other, the problem arises, in connection with planographic printing without the use of a dampening agent, that the ends of the printing plates are often also being printed, at least lightly. This occurs even though the ends of the printing plates are located in an area of the print image which actually should not be printed.